The invention relates to an apparatus for controlling the current through an electromagnetically actuatable injection valve in internal combustion engines. An apparatus is already known from German Patent Application P No. 26 12 914.6 for the electrical current controlled triggering of electromagnetic switching systems, in which a series circuit comprising a switching transistor, at least one injection valve and a measuring resistor is located between the lines supplying operating voltage. The free-running circuit thereby includes both the injection valves and the measuring resistor, so that the voltage drop across the measuring resistor is continuously a standard for the current through the magnetic valve.
Rapid switching of electromagnetic valves requires a rapid increase in electrical current, which because of given physical properties can be attained only by means of a relatively high flow of current. However, only a relatively low current flow is required for holding the magnetic valves open. Therefore, in the known apparatuses, a high current flow through the magnetic valves is sought at first, which then, during the holding phase of the magnetic valve, swings back and forth in a low-level range between two values. This means, first, that a threshold switchover is required for a threshold switch associated with the measuring resistor, and, second, that widely differing threshold values must be mastered. The lower threshold value is particularly problematic, because the measuring resistors are intended to have a very low value (50 milliohm) with a view to a low power loss, and therefore the voltage drop across the resistor is also very low, at the minimum electrical current prevailing during the holding phase.
Furthermore, the dependency of the attracting time of the magnetic valves on operating voltage has proved to be
disadvantageous, for differing operating voltages also effect differing increases in the pick-up current and therefore differing injection times.